Have you ever noticed that Boeing 737 engines have a weird shape? They look weird because they are flat at the bottom. But why are they flat? Is there some special reason for this?
Of course, there is a reason!
When the plane debuted, the Boeing 737 had rounded engines. But in 1985, Boeing decided to redesign the 737 to fit more passengers. The only way to do that was to stretch the airframe.
So, the Boeing 737-200, which had rounded engines, was stretched and Boeing started production of an extended version of the Boeing 737-200. As a result, Boeing launched the 737-300, 737-400, and 737-500 models, also referred to as the Boeing 737 Classic series.
But when the aircraft was stretched it changed the center of gravity and reduced the ground clearance. In order to resolve the problem of the new center of gravity, Boeing redesigned the engine pylons. The flattening of the engine’s nacelle provided extra clearance from the ground.
Of course, the engine itself is not flat, it is circular because the fan is circular. Only the bottom of the engine nacelle has been flattened.